Optical waveguides – Accessories – Attenuator
Reexamination Certificate
2001-10-24
2004-06-22
Lee, John D. (Department: 2874)
Optical waveguides
Accessories
Attenuator
C385S015000
Reexamination Certificate
active
06754431
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical fiber cross-connect switching. More particularly, it relates to load balancing in Dense Wavelength Division Multiplexing optical cross-connect systems.
2. Description of the Related Art
Associated with the information revolution is a need to increase by many orders of magnitude the rate of information transfer. This can be accomplished with optical fibers and the method of Dense Wavelength Division Multiplexing (DWDM), in which many wavelength channels, each including a different narrow band of wavelengths of light and each carrying different information, are multiplexed onto a single optical fiber using an optical multiplexer. Optical signals carried on the various wavelength channels may be separated at the output of the optical fiber with an optical demultiplexer.
Optical fiber cross-connect switches may be used to direct the optical signals on some or all of the wavelength channels on a particular optical fiber to other optical fibers. Such optical fiber cross-connect switches include those described in Ser No. 09/999,878, U.S. patent application Ser. No. 09/999,610, and U.S. patent application Ser. No. 10/002,310, all of which are incorporated herein by reference in their entirety. Hence, optical signals on the various wavelength channels on an optical fiber may have originated at separate locations and traveled different distances in optical fiber. Since light is attenuated during transmission through optical fiber by an amount typically proportional to the distance traveled in optical fiber, the various wavelength channels on an optical fiber may carry different power levels.
Optical amplifiers such as Erbium Doped Fiber Amplifiers (EDFA) can amplify a wide wavelength band (spanning many wavelength channels), and thus compensate for transmission losses in optical fibers. If the power levels on the various wavelength channels carried by the optical fiber are not nearly equal at the input to the optical amplifier, however, the wavelength channel or channels of highest power may saturate the gain. Under such circumstances, the lower power wavelength channels might not be sufficiently amplified.
A variable optical attenuator is an optical device with which the amplitude or power level of an input optical signal may be attenuated by a variable amount to provide an output optical signal of a desired amplitude or power level. The power levels of the various wavelength channels on an optical fiber may be substantially equalized in a “load balancing” or “load equalization” process in which each wavelength channel is routed through a separate variable optical attenuator. Variable optical attenuators are described, for example, in U.S. Pat. Nos. 5,864,643 and 6,130,984. These devices require the insertion of additional hardware into an optical network. The additional hardware may be expensive, requires additional physical space, and may introduce unwanted attenuation of the optical signals.
It would be desirable to incorporate the function of a variable optical attenuator into an optical network without the insertion of additional optical elements.
SUMMARY
A method of controllably attenuating a beam of light coupled into a port in accordance with an embodiment of the present invention includes directing the beam of light against a mirror, and controlling an orientation of the mirror such that a predetermined fraction of the beam of light is coupled into the port. The predetermined fraction is less than a maximum fraction corresponding to optimal coupling of the beam of light into the port. In one embodiment, this method is implemented with a variable optical attenuator including a first port, a second port, a mirror located to direct light output by the first port to the second port, and a controller coupled to the mirror to align it such that the predetermined fraction of light is coupled into the second port. The ports may be or include optical fibers.
In one implementation, the variable optical attenuator includes a second mirror located to direct to the second port light output by the first port and reflected by the first mirror. The controller is also coupled to the second mirror to align it such that the predetermined fraction of light is coupled into the second port. Use of two controllable mirrors in the optical path of the light beam allows independent control of the position and angle of incidence of the light beam on the second port.
Control of the mirror or mirrors in the variable optical attenuator may be accomplished by numerous methods. In one implementation, the power of light coupled into the second port is measured, and an orientation of a mirror is controlled to maintain the power at a predetermined level. In another implementation, an orientation of a mirror corresponding to the predetermined fraction described above is selected from a look-up table. In another implementation, an alignment beam of light is directed against a mirror, and the orientation of the mirror is controlled to direct the alignment beam to a predetermined position on a position sensing detector. The predetermined position corresponds to the predetermined fraction described above.
In another embodiment, a variable optical attenuator includes a first plurality of ports, a second plurality of ports, a first plurality of mirrors disposed on a first surface, a second plurality of mirrors disposed on a second surface, and a controller coupled to align each of the first plurality of mirrors and each of the second plurality of mirrors such that predetermined fractions of light output by the first plurality of ports are coupled into separate ones of the second plurality of ports. The predetermined fractions are less than maximum fractions corresponding to optimal coupling of light output by the first plurality of ports into the second plurality of ports. This embodiment may be employed, for example, to load balance DWDM wavelength channels.
A method of equalizing the power levels of (load balancing) a plurality of channels multiplexed on an optical fiber in accordance with an embodiment of the present invention includes demultiplexing the channels from the optical fiber to form a plurality of beams of light, with each beam of light formed from a separate channel, measuring the power level of each channel, directing each of the beams of light against a separate one of a plurality of mirrors, and controlling an orientation of one of the mirrors such that a predetermined fraction of the beam of light directed against that mirror is coupled into a port. The predetermined fraction is less than a maximum fraction corresponding to optimal coupling of the beam of light into the port.
Variable optical attenuators in accordance with embodiments of the present invention may be implemented in optical cross-connect switches. In such embodiments, the ports and mirrors of the variable optical attenuator may also support switching functions in the optical cross-connect switch. Optical cross-connect switches are typically designed and operated to achieve minimum insertion loss for all optical signals coupled into the switch. The inventors have recognized, however, that variable attenuation can be accomplished by separately controlling the insertion loss for the various optical signals by controllably misaligning mirrors used to switch the optical signals. Hence, the function of one or more variable optical attenuators may be advantageously integrated into an optical network without the insertion of additional optical elements.
REFERENCES:
patent: 5864643 (1999-01-01), Pan
patent: 6130984 (2000-10-01), Shen et al.
patent: 6222954 (2001-04-01), Riza
patent: 6374032 (2002-04-01), Mao et al.
patent: 6483962 (2002-11-01), Novotny
patent: 6522801 (2003-02-01), Aksyuk et al.
patent: 6618184 (2003-09-01), Jin et al.
patent: 2002/0114566 (2002-08-01), Fairchild et al.
patent: 2003/0007148 (2003-01-01), Moon et al.
patent: 2003/0012509 (2003-01-01), Chang et al.
patent: 2003/0026582 (2003-02-01), IN' T Hout et al.
Bakin Dmitry Vasily
Bryzek Janusz
Harwit Alex
Huang Cheng-Chung
Nasiri Steven Saeed
Intel Corporation
Lee John D.
LandOfFree
Variable optical attenuator does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Variable optical attenuator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Variable optical attenuator will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3327272